1. Field of the Invention
The present invention generally relates to masonry and concrete wall existing and new construction and, more particularly, is concerned with a method of strengthening, by using a composite fabric strap or a mixture of high strength random fibers and epoxy or the like, the masonry and concrete walls of existing construction having inadequate or no reinforcement and the masonry and concrete walls of new construction to permit an improved design.
2. Description of the Prior Art
As known to those skilled in the art, the majority of the existing masonry structures contain little or no steel reinforcement. These structures are referred to as Unreinforced Masonry (URM) structures. These walls are typically constructed with brick, hollow clay tile, or concrete masonry blocks. In addition, there are a large number of concrete walls with insufficient amounts of steel reinforcement. The latter can be cast-in-place or constructed as pre-cast modules of reinforced concrete walls which are tied together at the construction site (e.g. tilt-up walls and pre-cast concrete walls).
When the structures containing these walls are analyzed, these deficiencies (i.e. the lack of or insufficient amounts of steel reinforcement) are often identified. The presence of these deficiencies in existing construction requires that the walls be externally reinforced. Such is the case in seismic regions of the world, where a large number of these walls require strengthening.
Furthermore, in many frame structures, partition walls are used for division of the floor space. This type of construction is referred to as infill frame construction. Various types of solid or hollow bricks are placed within the plane of the frames to form a wall. In the event of an earthquake, these infill walls often fall apart and collapse, resulting in loss of life and property.
Yet a third category is the parapet wall around the perimeter of the roof of a building. These walls also often lack steel reinforcement and their collapse during earthquakes has been a major cause of loss of life and property.
It is therefore clear that there is a need for effective and economical techniques to strengthen these walls. Such techniques must increase the strength, stiffness, and ductility of the wall.
The methods commonly used to date for strengthening walls include the addition of a new reinforced concrete wall to one or both faces of the existing wall. The new walls include steel reinforcement which is tied to the surface(s) of the existing wall through anchor bolts. Then a layer of concrete (usually a few inches in thickness) is added or sprayed on top of the steel reinforcement. In essence, the old wall is sandwiched between the two new walls. This type of strengthening is not only time consuming, but it also results in a significant increase in the weight of the externally reinforced wall. Because the forces produced during an earthquake are proportional to the weight of the structure, this added mass results in larger forces being applied to the structure. Moreover, in many instances, the existing foundations of the structure cannot support the weight of the newly-added walls; this leads to further expenses to strengthen the foundation.
Consequently, an unfulfilled need still exists for effective and economical techniques to strengthen walls having inadequate or no reinforcement by increasing the strength, stiffness, and ductility of the walls.